let arr = [1, 2, 3, 4, 5, 6]

for (let item of arr) {
    console.log(item)
}

Object.prototype.d = 4
let obj = {
    a: '1',
    b: '2',
    c: '3'
}

let key = Object.keys(obj)

for (let key in obj) {
    if (obj.hasOwnProperty(key)) {
        console.log(key, obj[key])      
    }
    
}